Description

The network performance between the sites at IPP, FOM and UU is measured with a package called RTPL ( Remote Throughput, Ping and Load). This package does periodically net performance measurements between a set of hosts which can be specified by the user. A, so called, control host is used to start the net performance measurements at each of the participating hosts with a, so called, remote shell command. Also the results of the tests are send back via the remote shell command. See figure 1.

  

Figure: The control host starts the measurements at all hosts i by means of remote shells. The host i does the measurements to the hosts j The results are send back by host i to the control host.

Please note that a remote shell offers the possibility to start a command at a remote host. It also connects the I/O streams of the command at the remote host to the process, which started the remote shell, in a transparent way: that is for the process it seems that the command is running at the local host Security aspects are solved in various ways, depending from the remote shell command used. However in all cases there is no need to specify a user / password to get access to the remote host: this would deny a non-interactive run of the command at the remote host.

At each host i of the set the following performance tests are executed:

Throughput.

Formal definition from RFC 1224 [1]: ``The maximum rate at which none of the offered frames are dropped by the device''. It is a way to quantify the traffic flow which can be handled by a network connection. Default it is measured for the connections from the current host i to all other hosts, but it is also possible to skip connections. The throughput is measured with the public domain command netperf.

Roundtrip.

This Internet application is described in RFC 2151 [2] by the paragraph quoted below:

Ping, reportedly an acronym for the Packet Internetwork Groper, is one of the most widely available tools bundled with TCP/IP software packages. Ping uses a series of Internet Control Message Protocol (ICMP) [3] Echo messages to determine if a remote host is active or inactive, and to determine the round-trip delay in communicating with it.

The roundtrip time quantifies the response offered by a network connection. It will be measured, before the throughput, across the same connections as the throughput. The roundtrip time is measured with the system command ping.

Load.

This is expressed here as # fully active processes at a host. It is no network quantity, but it may help to explain unexpected performance decreases. The load is measured at the current host i, using the system command uptime.

The sampling of the results at the control host and the measurements at all hosts, participating in the tests, are performed by scripts in the scripting language Perl. Perl is a powerful scripting language which is available for many platforms, including Unix, Windows NT/9Xand MacOS.

The Perl script at the control host collects the results of the measurements for each host i and stores the results in ZIP compressed data files. The ZIP compression is used to reduce disk space and download time (see below).

The presentation of these results is Web based: a JAVA Applet is used to load the data from the files into the memory of the Web browser from a user looking at the results. Please note that an Applet is an architecture independent application, written in the JAVA programming language which runs in the so called JAVA virtual machine of the Web browser. The functionality to read (ZIP compressed) data files from a Web browser is a JAVA feature. This implies that access to the data is only possible via the Applet which had read the data.

The HTML scripting language JavaScript is used to dynamically present the user various HTML tables of the data. That is: the user selects a view at the data and the HTML code is generated on demand by JavaScript. JavaScript applies direct calls to Applet methods to obtain the required data for the HTML table to display. A direct call of Applet methods by JavaScript is a common functionality of most Web browsers. Further on the Applet can also be used to present various plots of the data to the user. The plots are displayed in a new window.

The following data files  are available to be viewed via the Web:

• The data of the last 7 days.
• For each week of the last half year a data file is available.
• The week mean values from the last year.
• The day mean values from the last year.
• The mean values, calculated at the periodic measurement times, for the days of the week, averaged during a quarter. The data are stored during a year.
• The mean values, calculated at the measurement times, for the workdays of the week, averaged during a month. The data are stored during a year.